1. Field of the Invention
This invention relates to musical sound producing device, and more particularly to musical sound producing device which changes data represented by MIDI signal to be supplied to MIDI sound sources and produces musical sound with pitches arbitrarily changed.
2. Description of the Prior Art
There is known MIDI (Musical Instrument Digital Interface) standard established for exchanging information between musical instruments such as synthesizer or electronic piano connected with each other. Electronic instruments provided with hardware according to MIDI standard and having functions of transmitting and receiving MIDI signal, serving as musical instruments control signal, are generally called as "MIDI equipments".
A MIDI signal supplied to MIDI equipment is serial data of transfer rate 31.25 [Kbaud]. One byte data of MIDI signal consists of 10 bits data including 8 bits for data, 1 bit for start bit and 1 bit for stop bit. Further, at least one status byte for indicating kinds of transferred data and MIDI channels and one or two data bytes introduced by the status byte are combined to form a message serving as musical information. Accordingly, one message generally consists of 1 to 3 bytes, and transfer time of one message ranges from 320 to 960 [.mu.sec]. These series of the messages constitutes musical instrument playing program. Some messages consist of only status byte or more than 3 bytes.
Constitution of note-on message and note-off message, included in channel voice message, will be described with reference to FIGS. 1A and 1B, as an example. In FIGS. 1A, the note-on message in the status byte 1 corresponds to operation of depressing a key of keyboard, for example, and the note-off message in the status byte 2 corresponds to operation of releasing the depressed key of keyboard. As shown in FIG. 2, note-on message and note-off message are generally used in pair with each other. Note-on message is expressed by "9h" (h:hexadecimal digit), and note-off message is expressed by "8h". Channel designates one of sixteen tones assigned to "0h-Fh". Note number in the data byte 1 indicates pitch, and designates one of 128 stages (0h-7Fh) of pitches which are assigned to 88 keys of piano in a manner that the center key of 88-key piano corresponds to the center of the 128 stages (0h-7Fh) of pitches. Velocity in data byte 2 designates one of 128 stages of intensity of sound (volume). Note-off message may be replaced with note-on message of the same channel and having velocity value of zero. According to the data format described above, MIDI equipment produces sound of designated pitch with designated volume. For example, when the messages shown in FIG. 1B are supplied, MIDI equipment outputs sound of tone designated by the channel data "0" with pitch designated by the note number "60" and intensity (volume) designated by the velocity data "65". The status byte 2 (indicating "80") subsequent thereto instructs terminating output of sound of tone "60" with volume "65". Therefore, if MIDI sound source module, amplifier and speaker are connected as shown in FIG. 3, MIDI equipment can produce desired musical sound, like electronic instruments.
In connection with music play by MIDI equipments, there is known pitch control device (key control device). Pitch control device changes note number value, set in note-on message of MIDI signal serving as instruments play program, by a change value (e.g., "1") and supplies MIDI signal of transposed songs to MIDI equipments. For example, when the messages shown in FIG. 1B are supplied, pitch control device changes the note number from "60" to "61", in response to key change instruction from user, and supplies the MIDI signal thus modified to MIDI equipments so as to reproduce transposed music songs. By applying such a device to karaoke system, pitch of accompaniment may be modified to adapt to key of singer. A pitch control device of this kind is described in Japanese Patent Application No. 02-147976.
However, pitch control device described above changes pitch for all tones uniformly, in response to user's key change instruction. Therefore, tone quality of some instruments may changed unnaturally. Particularly, pitch is uniformly changed to tones that do not require changes, such as rhythm instruments like drum, hand clapping in karaoke songs or sound effect like sound of falling rain. Therefore, transposition by such device gives unnatural feelings to user, compared with transposition in live performance.